1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method and a substrate manufacturing method.
2. Description of the Related Art
Since silicon carbide (SiC) has advantageous characteristics such as a wide energy band gap, a high dielectric strength voltage, and a high heat conductivity as compared with silicon (Si), silicon carbide attracts attention as an element material, particularly for an element of a power device. However, due to other characteristics of SiC such as a non-liquid state at normal pressure and a low impurity diffusion coefficient, it is difficult, as is known, to fabricate a crystal substrate or a semiconductor device by using SiC as compared with the case of using Si. For example, since a SiC epitaxial film is formed in a high temperature range of about 1500° C. to about 1800° C. as compared with a temperature range of 900° C. to 1200° C. in which a Si epitaxial film is formed, it is necessary to study technology for heat-resistant structures of SiC epitaxial film forming apparatuses and source material decomposition preventing methods. Furthermore, in the case of a substrate processing apparatus configured to form a SiC epitaxial film, since two elements (silicon (Si) and carbon (C)) are used to form a film, additional studies which are not necessary for a silicon film forming apparatus are required for ensuring the uniformities of a film thickness and a composition ratio and controlling a doping level.
As mass-production SiC epitaxial film forming apparatuses, pancake type apparatuses are widely sold in the market. Epitaxial films can be formed by arranging several substrates to about tens of substrates on a susceptor which is heated to a film forming temperature, for example, by high-frequency waves, and supplying a silicon-containing gas (hereinafter also referred to as a Si source gas), a carbon-containing gas (hereinafter also referred to as a C source gas), and a carrier gas to the substrates. Propane (C3H8) gas or ethylene (C2H4) gas is widely used as a C source gas, monosilane (SiH4) gas is widely used as a Si source gas, and hydrogen (H2) gas is widely used as a carrier gas. To control formation of silicon nuclei in a gaseous phase and improve crystalline quality, hydrogen chloride (HCl) gas may be added to a source gas, or a material including chlorine (Cl) in its formula such as trichlorosilane (SiHCl3) gas or tetrachlorosilane (SiCl4, silicon tetrachloride) gas may be used as a Si source (for example, refer to Non-patent Document 1).
However, such mass-production substrate processing apparatuses configured to form SiC epitaxial films have the following problems. FIG. 1 is an exemplary schematic view illustrating a relationship between a structure of a pancake type susceptor and positions of substrates. As shown in FIG. 1, the diameter and number of substrates that can be placed on the susceptor are limited to the diameter of the susceptor. Therefore, if the diameter of the substrates is large, the number and total area of the substrates that can be processed at a time are reduced. For example, in the case of FIG. 1, if the diameter of the substrates arranged on the susceptor is increased by a factor of 1.5, the number of the substrates that can be processed at a time is reduced from twenty to eight, and the total area that can be processed at a time is reduced by about 10%. Thus, for mass production with such a pancake type susceptor, it is necessary to increase the number of substrate processing apparatuses or the area of a susceptor of a substrate processing apparatus (that is, the footprint of a substrate processing apparatus); otherwise, production costs are largely increased.
Therefore, the inventors considered that: like in the case of a substrate processing apparatus used for forming a Si film, if one hundred or more substrates having a diameter of, for example, 300 mm are vertically stacked and are batch-processed by employing a vertical structure, an increase of production costs can be prevented without having to increase the number of substrate processing apparatuses or the footprint of a substrate processing apparatus. In such a vertical type substrate processing apparatus, a gas supply nozzle is installed in a reaction chamber to introduce a source gas and uniformly supply the source gas to stacked substrates. In this way, the source gas can be efficiently and uniformly supplied to a plurality of substrates which are vertically stacked, and thus the uniformity of a film thickness can be improved between the substrates and in the surfaces of the substrates.
[Non-patent Document 1] P. VAN DER PUTTE, L. J. GILING and J. BLOEM, “GROWTH AND ETCHING OF SILICON IN CHEMICAL VAPOUR DEPOSITION SYSTEMS; THE INFLUENCE OF THERMAL DIFFUSION AND TEMPERATURE GRADIENT”, Journal of Crystal growth, vol. 31, 1975, pp. 299-307.
However, if the above-described vertical structure is applied to a substrate processing apparatus configured to form a SiC epitaxial film so as to vertically stack a plurality of substrates and process the substrates at a time, there occur problems related with the decomposition temperature of a Si source gas. Although varying according to the composition of a Si source, the thermal decomposition temperature of monosilane (SiH4) generally used as a silicon source is known to be about 950° C. to 1050° C., and even tetrachlorosilane (SiCl4) including chlorine is known to be thermally decomposed at about 1150° C. to 1250° C. Generally, SiC is epitaxially grown at about 1500° C. to about 1800° C. Properties of Si source gases are exemplarily shown in FIG. 9.
In the case where the above-described vertical structure is applied to a substrate processing apparatus configured to form a SiC epitaxial film, a gas supply nozzle for supplying a Si source gas is installed in a reaction chamber in a manner such that the gas supply nozzle extends along a region where substrates are stacked for a batch process, that is, a region where substrates are arranged. For this reason, the inside temperature of the gas supply nozzle becomes equal to the inside temperature of the reaction chamber, that is, the inside temperature of the gas supply nozzle becomes higher than the decomposition temperature of the Si source gas. As a result, when the Si source gas is supplied into the reaction chamber, the Si source gas may decompose while passing through the gas supply nozzle, and thus the Si source gas may be insufficiently supplied into the reaction chamber. Moreover, due to the decomposition of the Si source gas, Si may be deposited on the inner wall of the gas supply nozzle; the inside of the gas supply nozzle may be clogged by deposited Si; an ejection hole formed in the gas supply nozzle may be clogged by deposited Si; and thus the Si source gas may not be supplied into the reaction chamber. In addition, Si deposited on the gas supply nozzle may enter the inside of the reaction chamber to contaminate the inside of the reaction chamber. In addition, since the inside temperature of the gas supply nozzle is higher than the melting point of extracted deposited Si, some of deposited Si may melt and flow to a substrate to cause a crystalline defect on the surface of the substrate.